Liquid salts of imidazole compounds have ionic conductivity, flame retardance, non-volatility, high polarity and solubility, and by making use of these properties, are expected to be used as electrolytes for fuel cell, secondary battery, capacitor, dye-sensitized solar cell and electrochromic device, or as ionic liquids having various functions useful for reaction media, catalyst, and chemical separation and reprocessing of nuclear fuel.
There are many examples of use of ionic liquids immobilized with a polymer. For example, JP11-306859A discloses a solid polymer electrolyte, a process for preparing the solid polymer electrolyte, and a lithium secondary battery and an electric double layer capacitor using the solid polymer electrolyte. Electric conductivity thereof is as high as 10−3 S·cm−1 which is usable for practical application. This patent publication says that by use of an ionic liquid, a solid polymer electrolyte comprising a fluorine-containing polymer, an imidazolium salt and a lithium salt is stable even in the air containing moisture, and since it does not contain a conventional electrolytic solution, namely an organic solvent, there is no problem with leakage and evaporation of a solution and a solid polymer electrolyte having high reliability and durability can be prepared. In addition, U.S. Pat. No. 5,296,318 discloses that fluorine-containing polymers are useful for electrolyte application.
Further, for example, J. Fuller et al. discloses, in J. Electrochem. Soc. (1997), 144(4), L67 to L70, a gel electrolyte in the form of rubber comprising an ionic liquid comprising a vinylidene fluoride/hexafluoropropylene copolymer and 1-ethyl-3-methylimidazolinium-trifurate or tetrafluoroborate as base components.
Also, J. Fuller et al. have made investigation with respect to a mixture comprising an ionic liquid or other imidazolinium salt and a vinylidene fluoride/hexafluoropropylene copolymer (Molten Salt Forum 5-6 (1998) 605-608). This mixture shows high electric conductivity, thermal stability and dimensional stability for applications to batteries, fuel cells and highly conductive polymer electrolytes.
Further, JP2005-176428A proposes an actuator element operable in the air or in vacuo by using a gel of carbon nanotube and ionic liquid as an active layer having conductivity and expandability and using a layer comprising an ionic liquid and a fluorine-containing polymer such as a vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride or perfluorosulfonic acid (NAFION: trademark of Du Pont) as a conductive layer.
From these examples, it is obvious that fluorine-containing polymers are useful as materials for polymer electrolytes. However since ionic liquids are inherently not compatible with fluorine-containing polymers, at present, fluorine-containing polymers used for these applications are limited only to polymers comprising vinylidene fluoride as a monomer unit.
JP2005-530894A discloses an electrolyte for an electro-optical device comprising an ionic liquid, and it is described that the electrolyte can be used for a solid film of electrochromic polymer. Though there is no description as to a polymer to be used, it can be considered that a fluorine-containing polymer having good electrochemical physical properties and optical transparency can be 1.5 used together with an ionic liquid.
In a mixture comprising a nonionic polymer and an ionic liquid, in order to make improvement in solving a problem that ion density is not high, JP2005-527667A discloses a process for preparing a cationic non-fluorine-containing polymer having amidinium group and a composition comprising an ionic liquid. However it is difficult to adopt such a process and composition since preparation of a polymer is carried out by a polymer reaction of a prepolymer and increase in a reaction ratio and refining are difficult. Also it is difficult to apply the mentioned process to preparation of a fluorine-containing polymer having heteroaromatic ring because synthesis of a fluorine-containing prepolymer is difficult.
With respect to fluorine-containing ionic liquids, for example, JP2003-62467A discloses an ionic liquid composition comprising 1-(2,2,2-trifluoroethyl-3-methylimidazolium trifluoromethanesulfonate. V. V. Rudyuk et al., J. Fluorine Chem., 125, pp. 1465-1471 (2004) discloses that after conversion of an imidazole compound into a potassium salt, when the potassium salt is allowed to react with CF2═CFCl under refluxing in dimethylacetamide, an imidazole compound in which N—K groups of the imidazole compound have been converted to N—CF═CFCl groups and N—CF2CFCl groups can be obtained. Further, it is disclosed in Y. L. Yagupolskii et al., J. Fluorine Chem., 126, pp. 669-672 (2005) and U.S. Pat. No. 2,861,990 that a pyrrole compound or an indole compound is allowed to react with fluoroalkene such as CF2═CF2, CF2═CFCl or CF2═CFCF3 in the presence of metallic potassium or metallic sodium, and a pyrrole compound or an indole compound, in which N—H groups thereof are added to fluoroalkene, can be obtained.
Further, for ionization of an obtained imidazole compound having a fluoroalkyl group, there is employed a method of anion exchange by substitution reaction of the compound with methyl iodide as disclosed in Y. L. Yagupolskii et al., J. Fluorine Chem., 126, pp. 669-672 (2005).
However, these are all compounds having no polymerizable group.